Tube bend

ABSTRACT

A tube bend has at least one bend zone and two outlet zones adjoining the latter on both sides. The tube bend has a different cross-sectional shape from the outlet zones with an identical flow cross section. The degree of expansion, as the ratio of the diameter of the component in the bending plane to the diameter of the blank in the bending plane, has a value between 1 and 1.1.

The present invention relates to a tube piece designed as a tube bend,with at least one bend zone and two outlet zones adjoining the latter onboth sides with in each case an end side for the application of pushingrams of an internal high-pressure tool which comprises a die with arecess forming the production cross section.

A method for manufacturing a tube bend is already known from Germandocument DE 43 22 711 C2. There, the tube section is bent beforeinternal high-pressure forming and upset axially during the internalhigh-pressure forming. In the process, the tube section undergoesenlargement of the average diameter, this expansion taking place overthe entire periphery relative to the central axis. Starting from a roundtube cross section and taking the ovality of the cross section in theregion of the tube bend brought about during bending into account, therequisite degree of expansion is greater in this region of the tubesection in relation to the average degree of expansion.

The invention has as an object the object of designing and arranging atube bend in such a way that stable cross-sectional enlargement isguaranteed during internal high-pressure forming.

According to this invention, the object is achieved by virtue of thefact that the bend zone has a different cross-sectional shape from theoutlet zones with an approximately identical flow cross section. Theresult of this is that the different cross-sectional shape guaranteesloading of the tube bend and at the same time a throttling effect of thebend zone is prevented owing to the constant flow cross section.

The axial pushing force exerted on the tube bend during manufacture ofthis internal high-pressure formed part serves, by virtue of the changedcross-sectional shape in the bend zone, to support the material flow,the changed cross-sectional shape preventing a buckling movement of thetube bend.

It is advantageous if the internal high-pressure tool for manufacturinga tube piece comprises a die with a recess forming the production crosssection of the tube bend, the recess having at least one bend zone andtwo outlet zones adjoining the latter on both sides. In this connection,the recess of the die has a different cross-sectional shape from theoutlet zones with an identical cross-sectional area which forms theproduction cross section. The recess thus formed, or the internalhigh-pressure tool thus formed, guarantees that the tube bend to beformed is acted on with the requisite axial force without a bucklingmovement of the tube bend, in particular in the region of the bendingplane or of the bend plane, taking place. The minimal degree of formingof the tube bend in the bending plane or bend plane guarantees that thetube bend bears against the recess of the die in the region of the bendzone, so that the pushing movement of the pushing rams does not giverise to a buckling movement, in particular of the tube bend inner side.In the case of internal high-pressure forming as known in the prior art,the inner side of the bend zone, that is the side with the smallerbending radius, would be upset owing to the pressure action alone as theshaped geometry provides for a smaller radius of curvature than theblank. Superimposing the axial pushing movement of the pushing ramsnecessary in places on this material upsetting leads to failure of thematerial wall. This is prevented by the tube bend which bears againstthe die in the bend zone, the bend being pressed against the die wall onaccount of the pressure action without upsetting forming having beencarried out beforehand.

An additional possibility is that an axis of symmetry of the bend zoneextends in a bending plane and, in the region of the bending plane, thedegree of expansion, as the ratio of the diameter of the component inthe bending plane to the diameter of the blank, in the bending plane, isbetween 1 and 1.1. The blank is consequently formed only slightly.

It is furthermore advantageous if the degree of expansion in the regionnormal to the bending plane is between 1 and 2, in particular between1.3 and 1.5. In this connection, it is advantageous if the degree offorming increases proportionally starting from the bending plane andreaches its maximum value toward the normal.

For this, it is also advantageous if a number of bend zones and a numberof bending planes are provided. In the manufacture of more complex tubebend shapes, a number of bend zones can be provided, each bend zonehaving its own bending plane. The changing cross-sectional shaping isthen adapted according to the course of the bending planes, whichguarantees the bearing according to the invention of each bend zone inthe region of the respective bending plane.

According to a preferred embodiment of the solution according to theinvention, provision is lastly made that a transition of thecross-sectional shape from each outlet zone to the bend zone extendscontinuously. The continuous cross-sectional adaptation between thecross-sectional shape of the outlet zones and the cross-sectional shapeof the bend zone guarantees minimal flow loss of the media flowing inthe tube bend.

It is of particular importance for the present invention that thecross-sectional shape of the bend zone and/or of the outlet zones is ofround, oval, rectangular or polygonal design.

In connection with the design and arrangement according to theinvention, it is advantageous if a tube piece blank with a diameter A isplaced into the recess of the die of the internal high-pressure tool andis acted on by the pushing rams. The tube piece blank is formed orexpanded to a desired diameter B in the region of the outlet zones, thetube piece blank being formed or expanded to a desired diameter C in thedirection parallel to the bending plane in the region of the bend zone,and the tube piece blank being formed to a desired diameter D in thedirection at right angles to the bending plane in the region of the bendzone. The degree of expansion as the ratio of C to A is set between 1and 1.1. Depending on material and material thickness, a greater degreeof expansion, that is greater forming, is possible within the bendingplane in the region of the critical bend zone without a bucklingmovement occurring. In this connection, the workpiece can already bearagainst the die with the inner wall part, that is with the wall partwith the smallest bending radius, in the region of the critical bendzone before the process. The minimal forming is generated in the bendingplane, in particular in the wall region with the largest bending radius,that is the outer wall region. The critical buckling movement in theinner wall region is consequently prevented. Larger forming operationswith a degree of forming appreciably greater than 1.1 (with regard tothe ratio of deformed size to blank size) cannot, however, be realizedwithin the bending plane. In the dimensioning of the degree ofexpansion, the elastic yield point of the material is also to be takeninto account, so that in particular the ratio of C to A can rise above1.1 and the bearing of the elastically expanded bend zone against thedie is nevertheless guaranteed.

It is furthermore advantageous if the degree of expansion as the ratioof D to A is set between 1 and 2, in particular between 1.3 and 1.5. Inthis connection, a degree of forming of 2, that is a twofold enlargementof the internal high-pressure formed part starting from the blank size,represents for the usual materials a maximum value which, depending oncross-sectional shape change, must be reached to guarantee a constantflow cross section.

Further advantages and details of the invention are defined by thepatent claims, explained in the description, and illustrated in thefigures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a longitudinal sectional illustration of a tube piece blankin the die;

FIG. 1 b is a view along the cross section C-C;

FIG. 2 is a longitudinal sectional illustration of an expanded tubepiece in the die, and

FIG. 2 b is a view along the cross section D-D.

DETAILED DESCRIPTION OF THE INVENTION

A tube bend blank 1 designed as a tube piece blank and illustrated inFIG. 1 has an axis of symmetry 1.6 and a diameter A which is constantalong the axis of symmetry 1.6. In this connection, the tube bend blank1 is bent by 90° starting from a cylindrical basic shape and has an axisof symmetry 1.6 which is correspondingly curved by 90°. The radius ofcurvature of the axis of symmetry 1.6 is approximately 1.5 times thediameter A.

The tube bend blank 1 thus formed has a bend zone 1.1 in the region ofthe curvature and a first cylindrical outlet zone 1.2 and a secondcylindrical outlet zone 1.3. At the end of the two outlet zones 1.2,1.3, the tube bend blank 1 comprises a first end side 1.2′ and a secondend side 1.3′, to which pushing rams 2, 3 of an internal high-pressureforming device are connected, which on the one hand serve for axialpressure action and on the other hand introduce the pressure medium. Thetube bend blank 1 is arranged within a die 4 which comprises a recess4.5 for receiving the tube bend blank 1. The tube bend blank 1 iscoupled to the pushing rams 2, 3 at its two end sides 1.2′, 1.3′. Inaddition to the recess 4.5, the die 4 comprises a further recess 6 whichadjoins the recess 4.5 radially and, according to FIG. 2, guarantees aspecial shaping geometry of the tube bend blank 1.

In the region of the bend zone 4.1, the recess 4.5 has in the bendingplane or bend plane the same diameter A as the tube bend blank 1.According to the cross-sectional illustration C-C, the recess 4.5 of thedie 4 has an appreciably larger diameter D (according to section D-D) inthe direction perpendicular to the bending plane or bend plane.

In the region of the two outlet zones 4.2, 4.3, the recess 4.5 of thedie has, differing from the bend zone 4.1, a cylindrical basic shape(not illustrated further) corresponding to the tube bend blank 1. In theregion of the two outlet zones 4.2, 4.3, the recess 4.5 has a largerdiameter B (according to FIG. 2) than the tube bend blank 1.Consequently, the tube bend blank 1 bears linearly with the bend zone1.1 against the die 4 or its bend zone 4.1 in the bending zone next tothe two pushing rams 2, 3.

In this connection, the cross-sectional shape of the recess 4.5, whichis circular in the region of the two outlet zones 4.2, 4.3, changes inthe region of the bend zone 4.1 according to FIG. 1 b to an ovalcross-sectional shape with the same cross-sectional area 4.4.

According to FIG. 2, the tube bend blank 1 is shaped into the tube bendand has the shape of the recess 4.5. In addition to the additionalradial shaping 5 in the region of the second recess 6 of the die 4, thetube bend blank 1 has in the region of the two outlet zones 1.2, 1.3been enlarged to the diameter of the recess 4.5 and has in the region ofthe two outlet zones 1.2, 1.3 a corresponding circular cross-sectionalshape (not illustrated further). In the region of the bend zone 1.1, thetube bend blank 1 has according to FIG. 2 b been shaped ovally accordingto the oval shape of the recess 4.5, the degree of expansion beingdesigned to be equal to 1 parallel to the bending plane and to increaseto a minimum dimension, that is maximum forming, in the direction atright angles to the bending plane.

During the shaping operation, the tube bend blank 1 is acted on withaxial pressure via the pushing rams 2, 3, with which sufficient materialflow for the forming, in particular in the region of the second recess 6or other recesses not illustrated here, is guaranteed. During the axialpressure action by the pushing rams 2, 3, the tube bend bears againstthe die 4 or its bend zone 4.1 with the bend zone 1.1 in the bendingplane.

1-7. (canceled)
 8. A tube piece comprising at least one bend zone, andtwo outlet zones adjoining the at least one bend zone on both sides,each of the outlet zones having an end side for application of pushingrams of an internal high-pressure tool including a die with a recessforming a production cross section, wherein the bend zone has adifferent cross-sectional shape from the outlet zones with anapproximately identical flow cross section, wherein an axis of symmetryof the bend zone extends in a bending plane, wherein, in a region of thebending plane, a degree of expansion, as a ratio of a diameter of theblank in the bending plane to a diameter of the component in the bendingplane, is between 0.9 and 1, and wherein a degree of expansion in aregion normal to the bending plane is between 0.3 and
 1. 9. A tube pieceas claimed in claim 8, wherein multiple bend zones and multiple bendingplanes are provided.
 10. The tube piece as claimed in claim 8, wherein atransition of the cross-sectional shape from each outlet zone to thebend zone extends continuously.
 11. The tube piece as claimed in claim8, wherein the cross-sectional shape of at least one of the bend zoneand the outlet zones is of round, oval, rectangular or polygonal design.12. The tube piece as claimed in claim 8, wherein the degree ofexpansion is between 0.6 and 0.8.
 13. The tube piece as claimed in claim9, wherein a transition of the cross-sectional shape from each outletzone to the bend zone extends continuously.
 14. The tube piece asclaimed in claim 9, wherein the cross-sectional shape of at least one ofthe bend zone and the outlet zones is of round, oval, rectangular orpolygonal design.
 15. The tube piece as claimed in claim 10, wherein thecross-sectional shape of at least one of the bend zone and the outletzones is of round, oval, rectangular or polygonal design.
 16. Aninternal high-pressure tool for manufacturing a tube piece comprising adie with a recess forming a production cross section of a tube bend, therecess having at least one bend zone and two outlet zones adjoining theat least one bend zone on both sides, wherein the recess of the die hasa different cross-sectional shape from the outlet zones with anidentical cross-sectional area forming the production cross section,wherein an axis of symmetry of the bend zone extends in a bending plane,wherein, in a region of the bending plane, a degree of expansion, as aratio of a diameter of the blank in the bending plane to a diameter ofthe component in the bending plane, is between 0.9 and 1, and wherein adegree of expansion in a region normal to the bending plane is between0.3 and
 1. 17. The tool as claimed in claim 16, wherein multiple bendzones and multiple bending planes are provided.
 18. The tool as claimedin claim 16, wherein a transition of the cross-sectional shape from eachoutlet zone to the bend zone extends continuously.
 19. The tool asclaimed in claim 16, wherein the cross-sectional shape of at least oneof the bend zone and the outlet zones is of round, oval, rectangular orpolygonal design.
 20. The tool as claimed in claim 16, wherein thedegree of expansion is between 0.6 and 0.8.
 21. The tool as claimed inclaim 17, wherein a transition of the cross-sectional shape from eachoutlet zone to the bend zone extends continuously.
 22. The tool asclaimed in claim 17, wherein the cross-sectional shape of at least oneof the bend zone and the outlet zones is of round, oval, rectangular orpolygonal design.
 23. The tool as claimed in claim 18, wherein thecross-sectional shape of at least one of the bend zone and the outletzones is of round, oval, rectangular or polygonal design.
 24. A methodfor manufacturing a tube piece comprising placing a tube piece blankwith a diameter A into a recess of a die of an internal high-pressuretool so as to be acted on by pushing rams, forming the tube piece blankto a desired diameter B in outlet zone regions, forming the tube pieceblank to a desired diameter C in a direction parallel to a bending planein the region of a bend zone, forming the tube piece blank to a desireddiameter D in the direction at right angles to the bending plane in theregion of the bend zone, and setting a degree of expansion as the ratioof the tube piece blank diameter A to the desired tube piece blankdiameter C between 0.9 and
 1. 25. The method as claimed in claim 24,wherein the degree of expansion as a ratio of A to D is set between 0.3and
 1. 26. The method as claimed in claim 25, wherein the degree ofexpansion is set between 0.6 and 0.8.